Multilayer interconnect (MLI) circuits are increasingly important in hybrid microcircuit electronics for the connection of silicon integrated circuits to the outside world. The MLI is composed of insulating dielectric layers separating metal conducting signal lines which are connected by vias through the layers. The silicon integrated circuit is generally mounted in a chip carrier on the top of the MLI circuit.
As the silicon circuits become larger and have higher speed, more demands are placed on the properties of the MLI. The layers should have a low dielectric constant and dissipation factor, high insulation resistance and breakdown voltage. They must be physically strong, moisture-resistant, pinhole- and blister-free and compatible with the electrode metallizations. The metallizations may be air-fired noble metals, silver or silver alloys, gold or they may be copper which requires nitrogen firing throughout manufacture. The metallization should be easily solderable and adhere well to the dielectric after thermal aging.
The property requirements are achieved both by design of the glass composition and the addition of certain fillers. The powdered ingredients are mixed with organic vehicle to form a paste or tape for laying down the layers. The layers and metallizations are fired either together or sequentially at a temperature sufficient to densify the glass and ceramic components.